A wraparound extension is an L or a U of kitchen and dining space wrapped around the original house. The decision is whether one indoor unit can throw into both legs, or whether the far corner needs a second indoor unit in the same open volume. Survey the plan and the glass before you buy a single large head for the nearest bit of wall. The outdoor unit has to live on a wall that still exists. An F-gas certified company commissions whatever layout the pipes allow.
The far leg under the lantern
People sit at the far end, under the lantern, while the indoor unit is on the original back wall blowing at the island. That near zone is fine and the far leg cooks. Two indoor units in one open room are the usual fix when the L is long. One unit is enough when the seating is all in one rectangle and the second leg is only a walkway. Draw where you eat and where you cook. The survey sizes the combined glass and the people, then places the heads. A bigger single kilowatt does not turn a corner. A larger unit on the island wall will not reliably cool the far leg. Air does not turn an L because the kilowatt is bigger. Place a second indoor unit for that leg, or accept that one end is the cooled zone. Shut rooms back in the original house are still separate. This job does not cool them. Original bedrooms remain a different job. Say the extension wraps the house, with a sketch or photos of both legs, the glazing, where you sit, and every outdoor wall that is still solid. Mark the hob.
A pad clear of the bi-folds, and two drains
The wrap has used the side and the rear. What remains may be a new flank wall, a bit of original side wall, or a pad in a smaller garden. The structure of a new wall full of doors may not take a bracket. A ground stand clear of the bi-folds is often the honest place, with airflow and a service side. One outdoor unit can feed two indoor units only inside the pipe length and height limits, and only if that one spot is lawful. In England, check Planning Portal conditions, especially noise toward the neighbour the wrap has moved you closer to. If the only spot fails, you cannot have two heads. You place one unit for the seats you use most. If pipe length, height and one lawful outdoor spot do not all work, the layout is one unit, or two singles with two outdoor positions you may not have.
The hob and the oven are part of the heat gain when you cook and cool at the same time. The extractor has to keep doing fumes. Do not aim the split into the extract, and do not hang it over the hob. Condensate from two indoor units means two drains or two pumps to gullies that the extension build should already have nearby. Ask which outdoor spot is lawful before you choose the indoor layout. Ask for a one-unit option and a two-unit option, with model codes and pipe lengths.
A second head only if this outdoor unit was specified for it
A new indoor unit added next year on this outdoor unit is usually not a mix-and-match unless the combination and the far-leg pipe were allowed at the start. As a 2026 illustration, one well placed unit is often in the low thousands including VAT, and a second head is a smaller uplift only when the outdoor unit and the drains were surveyed for it. The wrap is one open volume. Bedrooms behind shut doors need their own indoor units and their own pipe check.
Frequently asked questions
Will a larger unit on the island wall cool the far leg?
Not reliably. Air does not turn an L because the kilowatt is bigger. Place a second indoor unit for that leg, or accept that one end is the cooled zone.
Can both indoor units run on one outdoor unit?
Yes when pipe length, height and one lawful outdoor spot all work. If they do not, the layout is one unit, or two singles with two outdoor positions you may not have.
Does this cool the upstairs bedrooms?
No. The wrap is one open volume. Bedrooms behind shut doors need their own indoor units and their own pipe check.
Can the two indoor units run in opposite modes?
No. Same mode and close setpoints so they do not fight. Two remotes set to different modes will cancel each other in one open room. Ask how the two units should be set.
Core buying guides
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Related guides
Sources and further reading
How this guide was prepared
This guide was written by the Local AC Installers Editorial Team. We compare official guidance, legislation and established consumer information, separate general information from project-specific advice, and show publication dates and sources. We do not accept installer accreditation claims at face value.